What are synapses?
Specialized points of communication between a presynaptic (neuronal) and postsynaptic cell
List the types of synaptic connections.
- Nerve -> nerve cell
- Nerve cell -> muscle cell
- Nerve cell -> gland cell
- Sensory cell -> nerve cell
What are the two types of synaptic transmissions?
- Chemical
- Electrical
Describe the characteristics of chemical synapses.
- Complex
- Slow
- Unidirectional
- No intercellular continuity
Describe the characteristics of electrical synapses.
- Simple
- Fast
- Bidirectional
- Passive flow
What is the functional correlate of gap junctions in neurons?
Electrical synapses
What are gap junctions?
Specialized intercellular channels that permit direct cell-to-cell transfer of small molecules (ions, small metabolites…)
Where are gap junctions found?
In all tissue and cells; roles in development, homeostasis, regeneration
How many connexins form one connexon?
6 connexins
What is the role of electrical synapses in escape responses?
Build for speed (jump and fight response)
What is the main role of electrical synapses in smooth muscle?
Many cells contracting together (e.g., uterus in labor)
What is the role of electrical synapses in cardiac muscle?
Action potential spreads fast allowing the myocardium to contract as a unit
Describe the anatomy of chemical synapses.
- Presynaptic: swelling of axon terminal, large number of mitochondria, vesicles clustered at/near the edge
- Postsynaptic: electron-dense structure (postsynaptic density), receptors for neurotransmitters
What generates graded potentials in nerve-to-nerve chemical synapses?
Graded (depolarizing/hyperpolarizing) potential in the postsynaptic cells
What is presynaptic inhibition?
Selective excitation of the presynaptic axon that reduces Ca2+ entry and subsequent neurotransmitter release
What types of receptors are involved in chemical synapses?
- Ionotropic (fast) receptors
- Metabotropic (slow) receptors
Give examples of ionotropic receptors.
- Glutamate
- GABA
- Ach
- Glycine
Give examples of metabotropic receptors.
- Serotonin
- Dopamine
- Glutamate
- GABA
- Ach
- Histamine
What is the neuromuscular junction (NMJ)?
A peripheral synapse
